1. Field of the Invention
The present invention relates to an iron-nickel-chromium containing alloy wherein the ratios of nickel and chromium to iron, and the contents of the elements niobium, titanium and aluminum, are controlled to provide resistance to hydrogen environment embrittlement, high strength and moderate oxidation and corrosion resistance for elevated temperature service in hydrogen fueled rocket engine environments.
2. Description of Related Art
It is well known that alloys of iron, nickel and cobalt can be produced to provide high strength at elevated temperatures in severe environments. While nickel-based, iron-based and cobalt-based alloys can be produced to provide resistance to oxidation and hot corrosion, controlled coefficients of thermal expansion, high strength and good long time stability, an alloy exhibiting both resistance to hydrogen environment embrittlement and resistance to oxidation and corrosion has not been demonstrated. For rocket propulsion applications, especially for hydrogen fueled engine systems, these attributes are highly desirable. Resistance to hydrogen environment embrittlement allows the elimination of costly schemes for protecting hydrogen embrittlement susceptible materials from the hydrogen environment. Good strength in the temperature regime up to approximately 1200.degree. F. is required. Moderate resistance to oxidation and corrosion is required, primarily due to intermittent exposure to oxidizing atmospheres. The successful alloy for these applications must also be capable of being welded without deleterious microstructural changes.
Previous efforts to produce alloys for elevated temperature use have focussed on applications in the aircraft gas turbine or automotive industries.
U.S. Pat. No. 4,165,997 discloses an iron-nickel-chromium alloy incorporating at least columbium and titanium elements to provide a heat and corrosion resistance alloy, exhibiting strength retention, ductility, and resistance to oxidation.
U.S. Pat. No. 4,066,447 describes a low expansion nickel-iron alloy incorporating alluminum, titanium and other trace elements to insure satisfactory characteristics of thermal expansion coefficient, inflection temperature, yield strength and the like, where operating temperatures become elevated above 500.degree. F.
U.S. Pat. No. 3,663,213 describes a nickel-chromium-iron alloy wherein the nickel and iron contents are controlled to produce a strong age-hardening effect.
However, none of the alloys disclosed in the aforementioned U.S. patents are formulated such that they exhibit acceptable high hydrogen environment embrittlement resistance as well as corrosion and oxidation resistance.
Accordingly, it is an object of the present invention to provide a heat resistance alloy exhibiting high hydrogen environment embrittlement resistance as well as corrosion and oxidation resistance.
Another object of the present invention resides in a precipitation hardening, high strength alloy, characterized by a low, controlled coefficient of thermal expansion.
It is a further object of the present invention to provide heat resistant wrought articles such as plate, sheet, strip and forgings.
Another object is to provide articles in the form of castings.
Still another object is to provide articles which may be welded or joined without deleterious microstructural changes. cl SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a heat, embrittlement, corrosion, and oxidation resistance alloy comprising, in weight percent, 35.0 nickel, 10.0 chromium, 2.0 niobium, 1.0 aluminumm, and 1.0 titanium and the balance iron.
According to the present invention, niobium, alluminum and titanium levels have been adjusted in order to maintain strength and to avoid deleterious phase formation which decreases producibility and causes weld microfissuring.